A Multifunctional Skin‐Like Sensor Based on Liquid Metal Activated Gelatin Organohydrogel

Abstract

experience is dramatically improved. Despite the advantages, there are still existing challenges hindering the hydrogelbased soft electronics toward practical use. Particularly, most of the conductive hydrogels are comparing conductive nano-fillers (e.g., metal nano wire, [9,10] graphene, [11] carbon nanotubes, [12] and Perovskite [13] ) and polymer networks. [14,15] The mechanical mismatch between the rigid filler and soft polymer bulk will lead to concentrated internal stress and further affect the performance and lifetime of conductive hydrogel.In the past decade, liquid metals (LMs) [16][17][18] are emerging as novel conductive fillers for soft electronics, and among them, eutectic gallium and indium alloys (EGaIn) are the most widely used due to their negligible toxicity, low cost, and good thermal and electrical conductivity. More importantly, the melting point could be controlled below room temperature by appropriately adjusting the ratio of the Ga and In components, thus rendering EGaIn excellent ductility and fluidity to address the issues caused by rigid conductive fillers. Many studies have shown by using ultrasonic treatment, [19][20][21][22][23] EGaIn could be effectively dispersed in hydrophilic polymer precursor solutions, including polyvinyl alcohol, acrylic acid, and acryl amide. [24][25][26][27][28] After gelation process EGaIn is well distributed in polymer matrix as micro or nano size droplets, and the resulted hydrogels are endowed with unique thermal or electrical properties for different applications, such as tunable actuator or pressure sensor to discern bodily motions. However, it is noticeable that there is a reluctant use of peroxide initiator and toxic crosslinker for polymerization. The leaking risk of these agents and the poor degradability of the synthetic polymers have limited the hydrogels for bioengineering and in vivo biomedicals.Nowadays, with the increasing demand for ecologically sustainable and environment friendly materials, biopolymers are encouraged to replace the synthetic polymers to explore new advances in soft electronics. Generally, polysaccharide [29][30][31] and polypeptide [32,33] are the two typical types of biopolymers abundant in plants and animals, respectively. Since they are naturally occurred, biopolymers inherit the diverse structures and topologies in nature thus avoiding the toxic and complex polymeric synthesis process. In addition, due to their biodegradability and biocompatibility, biopolymers are extremely suitable for the use in wearable, [34] Gelatin, as a polypeptide-based biopolymer derived from animal resources, has a great potential to take the place of synthetic polymers for the development of next-generation electronic skin with enhanced biocompatibility and biodegradability. However, the soft and brittle nature of polypeptide hydrogel still remains as a challenge hindering its step to achieve skinlike properties and toward practical applications. Herein, a gelatin-based organohydrogel using liquid metal (LM) nanodroplets as functional filler...

Skin-like hydrogels: design strategy and mechanism, properties, and sensing applications

“…65,74,94 The smaller the TCR, the better the performance of skin-like hydrogel in temperature sensing. 95 The reason for the humidity perception of imitation skin is that water molecules in the air can form hydrogen bonds with hydrophilic groups (-COOH, -OH, -NH 2 ) in skin-like hydrogels. 77 Moreover, after humidity is absorbed by the skin-like hydrogel, the ion transport becomes faster and the resistance becomes lower.…”

Liquid Metal‐Based Organohydrogels for Wearable Flexible Electronics

“…[21][22][23] The formed Ga 2 O 3 layer can combine with different polar groups (SH, NH 2 , OH) through coordination interaction, [24,25] thus making Ga LM particles an alternative for chemical cross-linking agents. [15,26] Based on this characteristic of Ga LM particles, various Ga LMs-based hydrogel crosslinking networks can be constructed easily. [16,27,28] The interactions of EGaIn with LMIOs networks are revealed by X-ray photoelectron spectroscopy (XPS) spectra, as shown in Figure S5, Supporting Information.…”

Liquid metals nanotransformer for healthcare biosensors

“…When the substrate is deformed by the applied stresses, the LM will also accordingly deform, inducing changes in the cross-sectional area, conductive paths, and number of contact sites [151] , thus causing changes in the electrical signal of the monitoring circuit [Figure 4A iii]. In contrast to conventional rigid-filled materials, where changes in sensing signals such as resistance are achieved by the fracture of the substrate when subjected to tension [152,153] , the deformation mechanism of the LM causes minimal damage to the substrate and is nearly fully compliant [154] .…”